Baby not crawling

by Geraldine
(Alabama)

My 8 month old baby is not crawling. I have talked with other moms who have 7 and 8 month old children and all of their babies seem to be crawling and pulling up. My daughter likes to stand with support, but struggles to crawl when placed on her stomach. She can also push up on her hands when placed on her stomach, but does not do anything with her legs. Should I be concerned and what can I do to help her achieve this milestone?